In certain long range data communication and telemetry applications, the exchange of information occurs at a relatively lower data rate. In such applications, it can be advantageous to build a low to medium data rate system that possesses the characteristics of a widely variable data rate system, but with reduced power requirements.
For an RF communication system the power amplifier (PA) is commonly the main contributor to the power consumption of the system. The Peak to Average Power Ratio (PAPR) of the transmit signal impacts the required linearity and peak transmit power specification of the PA. That is, PAPR drives average power. By lowering the PAPR of the transmit signal, the power consumption, cost, and heat dissipation of the PA can be reduced.
There are many solutions for reducing PAPR. Some of these involve predicting peaks in the filtered transmit signal and reducing the peaks by modifying the pre-filtered transmit signal. These methods introduce distortion and are limited in the amount they reduce peak power.
A different method for reducing PAPR is to construct a transmit signal waveform that naturally has a low peak to average ratio. For Orthogonal Frequency Division Multiplex modulation, a method for reducing the PAPR is to pre-code the transmit modulation symbols using a Fourier Transform. This technique, used in Long Term Evolution (LTE) 4G cellular systems, essentially gives the multi-carrier OFDM signal the characteristics of a much lower PAPR single carrier signal.
Pre-coded OFDM or FDMA does not solve the problem since this type of modulation is designed for high rate (>1 bps/Hz) and is not extensible to lower data rates (<<1 bps/Hz) that operate at very low signal to noise ratios.
A reduced power system and method for transmission of data at low data rates is needed.